This invention relates to optical apparatus in general, and more particularly to an improved viewing field splitter for simultaneously viewing two sides of an object.
In copending application Ser. No. 339,860, filed Mar. 9, 1973 and assigned to the same assignee as the present invention, an optical projecting and scanning apparatus useful in producing integrated circuits is disclosed. The disclosed apparatus requires alignment between a mask and a semiconductor wafer. Alignment is carried out by an operator adjusting controls to affect relative motion between the wafer and mask. However, in order for the operator to properly carry out this alignment, he must be able to observe the results of the movement which he causes at the wafer. The aforementioned application discloses two viewing systems for making such alignment. One, a coarse viewing system, is the subject of an application Ser. No. 509,597, filed Sept. 26, 1974 by D. A. Markle, J. D. Buckley and R. E. Casas and assigned to the same assignee as the present invention. The second is a fine viewing system which permits simultaneously viewing two areas on the mask for fine alignment and which is disclosed and claimed herein.